Microtitration wells have become a standard part of most immunoassay procedures. Such wells can be used individually or connected together, e.g., in the form of strips or discs, or in the form of conventional 96 well trays See, e.g., U.S. Pat. No. 4,154,795. Given their standard size and configuration many devices have been manufactured that are adapted to hold, transfer, fill and/or empty, and otherwise use such wells in a variety of ways.
In some applications membranes have been placed onto the bottoms of open-bottomed wells and held in place by heat sealing, gluing, or sonically welding the membrane to the bottom surfaces of the walls of the well. See, e.g., U.S. Pat. No. 4,407,943. Such membranes have been described as being useful as supports, in order to retain one or more reaction components within the well, and for allowing sample and other solutions to flow through the membrane.
In addition to their use to support reactants, membranes are also frequently used for their ability to filter solutions, e.g., to remove particulates from the solution. The Minifold.TM. micro-sample filtration manifold available from Schleicher & Schuell, Inc., Keene, N.H., involves the use of filter discs overlaid onto silicone O-rings in a sample well plate. A separate filter support plate is then aligned over the sample well plate and the two plates clamped together. After use, i.e., application of vacuum and introduction of samples, the plates can be separated again, leaving the filter discs in place resting on top of the filter support plate.
Disadvantages to the use of membranes that are adhered to the bottom of open wells can include poor initial adhesion, loss of adhesion over time (i.e., stability), incompatability of adhesives and other such materials with either the wall or membrane materials and/or with components of the samples themselves, the difficulty inherent in actually adhering each membrane to each well, leakage of solutions at poorly adhered areas, and well-to-well "cross talk", i.e., solutions being absorbed by the membranes of adjacent wells due to the close physical proximity of membranes, thereby leading to inaccurate or incorrect readings.